20.
se apeleaza la rel. : n= m :M in care n= nr. de moli ;m=masa subst.
M=masa molara
a. n=m:M
m=n.M
m=5moli . 28g/moli=140g N2
b. m=2moli . 238g/moli=476 g U
c. m=3moli .56g/moli=168g Fe
d. m=4moli .59g/moli=236 g Ni
e. m=10000moli . 38g/moli=380000g F2
f. m=2500moli .20g/moli=50000g Ne
21.
a. 1mol Mg--------6,023 .10 ²³atomi
2moli Mg------------x
x=2 . 6,023. 10²³ atomi =
b. 1mol Ag--------6,023 .10²³ atomi Ag
0,5 moli Ag---------y
y=0,5 . 6,023.10²³ atomi Ag=
c. 1molAg---------6,o23.10²³ atomiAg
500 moli Ag--------z
z=500. 6,023 .10 ²³ atomi=
d. se afla nr. de moli de C------> n=m:M= 120g : 12g/mol=10 moli C
1mol C-----------6,023.10²³ atomi
10 moli----------x
x=10.6,023.10²³ atomi=
e. 120kg=120000g C
n=120000g: 12=10000 moli C
1mol C-----------6,023.10 ²³ atomi
10000moli--------x
x=10000. 6,023.10²³ atomi=
f. n=3,5g: 7g/moli= 0,5 moli Li
1mol Li------------6,023.10²³atomi
0,5moli------------x
x=0,5. 6,023.10²³ atomi
24. X Z=6 ; A=12
X Z=6 ; A=14 X=C
19.
a. n=m : M
n= 6g : 1g/molde atomi=6 moli de atomi H
b. n= 40g : 20g/moli=2 moli Ca
c. n=60000g : 16g/moli de atomi=3750 moli de atomi O
d. n=15000g : 31g/moli de atomi=483,8 moli de atomi P
